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Synthroid vs. Levothroid

Reviewed on 4/17/2019

Are Synthroid and Levothroid the Same Thing?

Synthroid (levothyroxine sodium) and Levothroid (levothyroxine sodium) are replacements for hormones produced by the human thyroid gland used to treat hypothyroidism (low thyroid hormone).

Synthroid is also used for pituitary TSH suppression.

Levothroid is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.

What Are Possible Side Effects of Synthroid?

Common side effects of Synthroid include:

Notify your doctor if you experience serious side effects of Synthroid including rapid heartbeat, fluttering in your chest, or chest pain.

What Are Possible Side Effects of Levothroid?

Common side effects of Levothroid include:

  • hair loss during the first few months of treatment. This side effect is usually temporary as your body adjusts to Levothroid.

Contact your doctor if you experience serious side effects of Levothroid including:

  • headache,
  • sleep problems (insomnia),
  • feeling nervous or irritable,
  • fever,
  • hot flashes,
  • sweating,
  • pounding heartbeats or fluttering in your chest,
  • changes in your menstrual periods,
  • appetite changes, or
  • weight changes.

What Is Synthroid?

Synthroid (levothyroxine sodium) is a synthetic compound identical to T4 (levothyroxine) produced by the human thyroid gland used to treat hypothyroidism due to many causes (for example):

  • thyroid removal,
  • thyroid atrophy,
  • functional T4 deficiency,
  • radiation treatment of the thyroid,
  • and other causes).

Synthroid is also used for pituitary TSH suppression.

What Is Levothroid?

Levothroid (levothyroxine sodium) is a replacement for a hormone that is normally produced by your thyroid gland to regulate the body's energy and metabolism used to treat hypothyroidism (low thyroid hormone). Levothroid is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.


Hyperthyroidism Symptoms and Treatment See Slideshow

What Drugs Interact With Synthroid?

Synthroid may interact with ferrous sulfate iron supplements, sucralfate, and antacids.

Synthroid may also interact with dopamine/dopamine agonists, glucocorticoids, octreotide, aminoglutethimide, amiodarone, iodide, lithium, methimazole, propylthiouracil (PTU), sulfonamides, tolbutamide, orlistat, clofibrate, oral contraceptives, estrogens, heroin/methadone, 5-fluorouracil, mitotane, tamoxifen, furosemide, heparin, hydantoins, nonsteroidal anti-inflammatory drugs (NSAIDs), salicylates, carbamazepine, phenobarbital, rifampin, beta-adrenergic antagonists, anticoagulants, antidepressants, antidiabetics, cardiac glycosides, cytokines, growth hormones, ketamine, bronchodilators, radiographic agents, sympathomimetics, chloral hydrate, diazepam, ethionamide, lovastatin, metoclopramide, 6-mercaptopurine, nitroprusside, para-aminosalicylate sodium, perphenazine, resorcinol (excessive topical use), and thiazide diuretics.

What Drugs Interact With Levothroid?

Levothroid may interact with ferrous sulfate iron supplements, sucralfate, and antacids.

Levothroid may also interact with calcium carbonate, sodium polystyrene sulfonate, and cholesterol-lowering drugs.

How Should Synthroid Be Taken?

Synthroid is prescribed in tablets that range from 25 to 300 mcg in strength and is usually taken once a day with a full glass of water (about 8 ounces) 30 to 60 minutes before breakfast for best adsorption into the body. Children can take the medicine if the tablet is crushed and put into about 1 to 2 teaspoons of water; do not store or delay giving this crushed pill suspension. Doctors often may have to slowly increase the dose; patients should not increase or decrease this medication themselves. Because some preparations of the drug may contain iodine or lactose, patients should tell their doctors about such allergies or reactions to these components. Many drugs can inhibit Synthroid's adsorption by the body; other medications may increase or decrease its effectiveness once it is adsorbed. Providing a complete list of medications to the doctor will help with getting the correct dose established for each individual patient. Pregnant and lactating females need to discuss the dose and use of this medication with their caregivers.

How Should Levothroid Be Taken?

For adult hypothyroidism, Levothroid is started at 12.5-125 mcg/day taken orally. Dose may differ with individuals based on age, the presence of cardiovascular disease, tolerance, side effects, and blood levels of thyroid hormone. It may take one to three weeks before effects are seen.


Where is the thyroid gland located? See Answer

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RxList. Synthroid Side Effects Drug Center
RxList. Levothroid Side Effects Drug Center.

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